open the box and check it out - here's inside the box [minus the grease] when it's just sitting in neutral - when it locks up the pawl is jamming between the 2 forks - the spring in there may be messed up, or the forks or pawl may be worn, or as suggested above you most likely have the arms down to the trans a bit out of adjustment

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature we find it attached to the rest of the world" John Muir
"When we tug a single thing on an old truck, we find it falls off" me
Some TF series details & TF heater pics & Rust-a-holics Unanimous parking lot